An electronic device may include an interface to communicate with other another electronic device using a communications bus. In order to send and receive signals on the communications bus, the interface may include a plurality of input/output (I/O) driver circuits configured to drive lines of the communications bus, such as by pulling up and down the levels of output voltages to respective logic high and logic low output voltage levels. In order to communicate with a wide variety of other electronic devices, the I/O driver circuits may be configured with different drive strengths for switching the output voltages from rail-to-rail (i.e., between the logic high and low logic voltage levels).
The I/O driver circuits may be subjected to testing to determine whether the I/O driver circuits meet certain DC parametric qualification requirements. Two DC parametric qualification requirements are the high output voltage level (VOH) requirement and the low output voltage level (VOL) requirement. The high output voltage level VOH may be the minimum accepted positive high output voltage level, and the low output voltage level VOL may be the maximum accepted positive low output voltage level. That is, if an I/O driver circuit generates its output voltage at a logic high level that is below the high output voltage level VOH, the output voltage may not be recognized as being at the logic high level by another device with which the I/O driver circuit is communicating. Similarly, if the I/O driver circuit generates its output voltage at a logic low level that is above the low output voltage level VOL, the output voltage may not be recognized as being at the logic low level by the other device with which the I/O driver circuit is communicating. In order to ensure signal integrity, the I/O driver circuits of a device may be subjected to VOH and VOL parametric testing to verify that the I/O driver circuits are generating output voltages that meet the VOH and VOL qualification requirements.
Some VOH and VOL parametric testing may use an external testing device (e.g., automatic test equipment (ATE)) that reads an output voltage generated by an I/O driver circuit. During VOH parametric testing, a test vector may generated to cause the I/O driver circuit to generate its output voltage at a logic high level. The external ATE may keep a current sink equivalent to the drive strength of the I/O driver circuit while the I/O driver circuit is driving the output voltage at the logic high level. The external testing device may read the output voltage at the logic high level and compare it with the VOH level to determine whether the I/O driver circuit meets the VOH qualification requirement. Similarly, during VOL parametric testing, a test vector may be generated to cause the I/O driver circuit to generate its output voltage a logic low level. The external ATE may keep the a current source equivalent to the drive strength of the I/O driver circuit while the I/O driver circuit is driving the output voltage at the logic low level. The external testing device may read the output voltage at the logic low level and compare it with the VOL level to determine whether the I/O driver circuit meets the VOL qualification requirement.
Since electronic devices of a same type (for example a particular memory device) may be produced in large quantities at or around the same time, a large number of external testing device are needed in order to test the large number of devices at the same time. In addition, the number of devices that can be tested in parallel may depend on a total number of available tester channels. Also, use of the external testing devices may require frequent cleaning of probe/tester tips after completion of a certain number of landings on dies as specified by tester requirements. In general, the added test costs and test time due to the use of external testing devices may increase the overall product cost of the electronic device. As such, an on-die solution for performing VOH and VOL parametric testing may be desirable.